Developing baths for photographic films comprise developing agents that are reducing compounds. As it is used, the developing bath becomes depleted in developing agent due to the development itself(redox reaction), and also due to aerial oxidation. This decrease of developing agent concentration causes a reduction of bath activity. In order to maintain bath activity, the bath has to be regularly replenished so as not to alter the quality of the developed products. However, it is desirable to replenish it so as to compensate solely for the variation of developing agent concentration. For this reason, regular and fast measurement of developing agent concentration in developing baths is desired.
Procedures for measuring the concentration of developing agents are known that include using a voltammetric method. Three-electrode cells are used to take measurements; they comprise three electrodes not fixed one to another. The operator who carries out the measurement arranges the electrodes in relation to one another in a position that allows correct measurement. One problem that occurs with this use is that the variation of position of the electrodes in relation one to another causes variations of the measurements. Another problem that occurs with this type of cell is that the measurement cannot be taken directly in the solution containing the developing agents. The solution is sampled and added into the cell. But the reaction continues to take place in the time that the solution is sampled and added into the cell. Thus the measurement that is taken in the cell does not allow the developing agent concentration in the developing bath to be obtained accurately. Furthermore, aerial oxidation can take place during the sampling.
On the other hand, procedures for measuring developing agent concentration that include using a voltammetric method use expensive apparatuses, which also requires operators to know about the chemical reactions that are taking place in developing baths and a certain number of adjustments.